You might have to define a hostel, as there exist places that offer accomodation for free (e.g. shelters for homeless people), but are not open to anybody, particularly not to tourists.
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gerritOct 9 '12 at 21:27

3

The cheapest guest house I stayed in was cheaper than the cheapest hostel. Does it have to be a hostel?
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Peter HahndorfOct 9 '12 at 21:27

Well, I'm asking about younth hostels only, it is, a place where travellers can spend a night in a bed for some money. I don't consider places that offers accomodation for free because these places are not tourism-oriented or require a friendship relationship (not just an economic transaction).
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IvanOct 10 '12 at 7:18

2

@ Peter Hahndorf - Me too, the cheapest was, I believe 50 rupees, which is just under one US dollar. It wasn't just one place but several which I can all list with corresponding prices (if needed). (EDIT: will change my comment to answer when I get some free time since these guest houses are cheaper then the one in Mark Mayo's answer.)
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John DoeOct 10 '12 at 17:50

The $1 dorm beds are in a thatched-roof hut that is partially open to
the elements. It appears that you do get a mattress, pillow, towel,
and even a mosquito net, but that’s it. There’s also no proper locker
system out there so you have to leave your valuables at reception when
you are away.

Nighttime average low temperatures are steady, ranging from 79F/26C in
March to 68F/20C in January, and it’s always humid, so it might not be
too comfortable on the warmest nights, but at least you’ll never be
cold.

Also, the dorm beds are right next to the kitchen, so you need to be
prepared for some noise and smells while you are saving all that
money.

So you really do get most of the normal benefits of staying at a
hostel, even for this ridiculously low price. Want something better,
Mr. Moneybags?

If you can afford US$6 per night you can get a “standard single” room
of your own, ranging up to a “deluxe triple” room for US$13.

You can’t book the $1 dorms online, but you can book all the other
private rooms from their website. I’m told you can reserve the $1
dorms by emailing them, so you won’t have to just roll the dice and
hope one is open.

Lest you think the Garden Village is just trying to get people stuck
in some remote place to sell them food and drinks, it is actually very
well located, only a few blocks from Pub Street and the main tourist
district of Siem Reap. Also, they have a good and cheap restaurant,
plus 50-cent Angkor draft beers available all day at their sunset
rooftop terrace.

Cheapest I've come across anywhere in my travels was Utopia Guesthouse in Sihanookville, Cambodia. There you can stay in their dorm room for FREE (yup, costs nothing), or I think i paid $4 for a private room there.

Don't get much cheaper than that! it's a pretty fun place to stay too, if you're into the party-type vibe.

Actually, just looked them up, seems they charge $1 for a dorm bed these days. Inflation huh.